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505-555 (Easy)|   Long Passage|   Science|         
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In most earthquakes the Earths crust cracks like porcelain. 14 Sep 2020, 09:03
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6. The passage suggests that which of the following must take place in order for any earthquake to occur?
I. Stress must build up.
II. Cool rock must descend into the mantle.
III. A fracture must occur.
Show more

Query on II

WHy II is not correct?

Quote:
The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.
Show more
If the rock does not descend how the fracture can happen ultimately.

SO if III is true , i think II must also be true.
Otherwise without descend why the rock would fracture as it is more ductile before descend into mantle.

please clarify GMATNinja VeritasKarishma AjiteshArun carcass sayantanc2k saswata4s Skywalker18
please suggest
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In most earthquakes the Earths crust cracks like porcelain. 14 Sep 2020, 22:47
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Quote:
6. The passage suggests that which of the following must take place in order for any earthquake to occur?
I. Stress must build up.
II. Cool rock must descend into the mantle.
III. A fracture must occur.

Query on II

WHy II is not correct?

Quote:
The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.
If the rock does not descend how the fracture can happen ultimately.

SO if III is true , i think II must also be true.
Otherwise without descend why the rock would fracture as it is more ductile before descend into mantle.

please clarify GMATNinja VeritasKarishma AjiteshArun carcass sayantanc2k saswata4s Skywalker18
please suggest
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Hi imSKR,

The question is: "The passage suggests that which of the following must take place in order for any earthquake to occur?" That is, this question is not limited to deep quakes. That's the reason statement II is not correct (it doesn't apply to quakes other than deep quakes, so it can't be the answer to a question about "any earthquake").
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In most earthquakes the Earths crust cracks like porcelain. 01 Jan 2021, 07:33
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But if the earthquake is a deep event,then the time interval between P and S should be large.Isn't that so?Then why is option A wrong?
If the earthquake is a deep event, then yes, the time interval will always be large. However, that is different than saying that if the time interval is large, the earthquake MUST have been a deep event!

The question asks about a large gap between P and S waves when measured from "a given location." The problem is that we have no idea where that location is in relation to the epicenter of the earthquake. If the location is very close to the epicenter and the gap between P and S waves is large, we can infer that the earthquake was a deep event. However, if the location is far away from the epicenter (e.g., Paris to Berlin), then a large gap could just be the expected result from a regular, more shallow earthquake.

Because we don't how close the "given location" is to the epicenter of the earthquake, we cannot infer that a gap between P and S waves at that point means that the earthquake was a deep event. Eliminate (A).

I hope that helps!
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Respected GMATNinja Sir,

I got only this question wrong and I am unable to wrap my head around options A and C, even after going through your above-mentioned explanation.

What I understood from the passage:
Both the time intervals of P-S and difference in intensity say that we have 2 kinds of earthquakes - 1. Shallow ones, in which focus is just beneath epicenter and 2. Deep ones, in which focus is hundreds of kilometers down.

Now,
Quote:
3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(C) The earthquake focus was distant.
Show more

I am not able to understand on what basis should I eliminate option A because, in the passage, 2nd point mentions that such events are deep ones in which focus is way beneath the epicenter. I am finding options A and C equally correct. :(
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In most earthquakes the Earths crust cracks like porcelain. 15 Jan 2021, 09:06
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Question 3


sssanskaar
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Ambika02
But if the earthquake is a deep event,then the time interval between P and S should be large.Isn't that so?Then why is option A wrong?
If the earthquake is a deep event, then yes, the time interval will always be large. However, that is different than saying that if the time interval is large, the earthquake MUST have been a deep event!

The question asks about a large gap between P and S waves when measured from "a given location." The problem is that we have no idea where that location is in relation to the epicenter of the earthquake. If the location is very close to the epicenter and the gap between P and S waves is large, we can infer that the earthquake was a deep event. However, if the location is far away from the epicenter (e.g., Paris to Berlin), then a large gap could just be the expected result from a regular, more shallow earthquake.

Because we don't how close the "given location" is to the epicenter of the earthquake, we cannot infer that a gap between P and S waves at that point means that the earthquake was a deep event. Eliminate (A).

I hope that helps!

Respected GMATNinja Sir,

I got only this question wrong and I am unable to wrap my head around options A and C, even after going through your above-mentioned explanation.

What I understood from the passage:
Both the time intervals of P-S and difference in intensity say that we have 2 kinds of earthquakes - 1. Shallow ones, in which focus is just beneath epicenter and 2. Deep ones, in which focus is hundreds of kilometers down.

Now,
Quote:
3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(C) The earthquake focus was distant.

I am not able to understand on what basis should I eliminate option A because, in the passage, 2nd point mentions that such events are deep ones in which focus is way beneath the epicenter. I am finding options A and C equally correct. :(
Show more
Question 3 is also discussed in this post, but read below for further explanation.

Imagine the following scenarios:

    1) There is a shallow earthquake in Paris, and you measure the time between P and S waves while you're standing in Paris.

      In this scenario, there would be a very SHORT time in between P and S waves, because you're close to the focus of the earthquake.

    2) There is a deep earthquake in Paris, and you measure the time between P and S waves while you're standing in Paris.

      Now, there would be a LONG time between P and S waves, because the focus of the earthquake is deep under the earth.

    3) There is a shallow earthquake in Paris, and you measure the time between P and S waves while you're standing in hundreds of miles away in Berlin.

      There would be a LONG time between P and S waves, because the focus of the earthquake is far away.

    4) There is a deep earthquake in Paris, and you measure the time between P and S waves while you're standing in hundreds of miles away in Berlin.

      There would still be a LONG time between P and S waves, because the focus of the earthquake is far away.

Question 3 asks us what we can infer if there is a LONG time in between P and S waves. You can see from above that there would be a long time in between the waves in scenarios 2), 3), and 4).

Scenarios 2) and 4) involve deep earthquakes, but scenario 3) involves a shallow earthquake. So, we can't infer that a long time between P and S waves means that the earthquake is deep -- all we can say is that the focus of the earthquake is far away.

(A) is out for question 3, and (C) is the correct answer.

I hope that helps!
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In most earthquakes the Earths crust cracks like porcelain. 18 Feb 2021, 08:51
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Dear GMATNinja

3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(B) The earthquake was a shallow event.
(C) The earthquake focus was distant.
(D) The earthquake focus was nearby.
(E) The earthquake had a low peak intensity.

I can pick the right choice thank to this information "Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus". However, I also confused for choice A until I read your below explanation. Thank you very much.

But I have an unclear point: Where does the passage mention or imply that the method of Wadati used to measure intervals is taking these mesurements at different locations? such as your example at earlier explanation: "Let's say an earthquake has an epicenter in Paris (sorry, Paris). If you measured the time interval between (P) and (S) waves at a point very close to Paris -- maybe just outside the city -- you would expect the time gap to be very small, because the faster (P) wave hasn't had time to get too far ahead of the slower (S) wave.
What if you measured that time interval at a point far away from Paris -- maybe in Berlin? Now you would expect the time gap to be larger, because the (P) wave has raced ahead of the (S) wave with each passing kilometer."

In deed, if the passage has such implication, I would not have confused when elimated A



GMATNinja
Ambika02
But if the earthquake is a deep event,then the time interval between P and S should be large.Isn't that so?Then why is option A wrong?
If the earthquake is a deep event, then yes, the time interval will always be large. However, that is different than saying that if the time interval is large, the earthquake MUST have been a deep event!

The question asks about a large gap between P and S waves when measured from "a given location." The problem is that we have no idea where that location is in relation to the epicenter of the earthquake. If the location is very close to the epicenter and the gap between P and S waves is large, we can infer that the earthquake was a deep event. However, if the location is far away from the epicenter (e.g., Paris to Berlin), then a large gap could just be the expected result from a regular, more shallow earthquake.

Because we don't how close the "given location" is to the epicenter of the earthquake, we cannot infer that a gap between P and S waves at that point means that the earthquake was a deep event. Eliminate (A).

I hope that helps!
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In most earthquakes the Earths crust cracks like porcelain. 23 Feb 2021, 16:34
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TrungTiger
Dear GMATNinja

3. It can be inferred from the passage that if the S waves from an earthquake arrive at a given location long after the P waves, which of the following must be true?
(A) The earthquake was a deep event.
(B) The earthquake was a shallow event.
(C) The earthquake focus was distant.
(D) The earthquake focus was nearby.
(E) The earthquake had a low peak intensity.

I can pick the right choice thank to this information "Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus". However, I also confused for choice A until I read your below explanation. Thank you very much.

But I have an unclear point: Where does the passage mention or imply that the method of Wadati used to measure intervals is taking these mesurements at different locations? such as your example at earlier explanation: "Let's say an earthquake has an epicenter in Paris (sorry, Paris). If you measured the time interval between (P) and (S) waves at a point very close to Paris -- maybe just outside the city -- you would expect the time gap to be very small, because the faster (P) wave hasn't had time to get too far ahead of the slower (S) wave.
What if you measured that time interval at a point far away from Paris -- maybe in Berlin? Now you would expect the time gap to be larger, because the (P) wave has raced ahead of the (S) wave with each passing kilometer."

In deed, if the passage has such implication, I would not have confused when elimated A



GMATNinja
Ambika02
But if the earthquake is a deep event,then the time interval between P and S should be large.Isn't that so?Then why is option A wrong?
If the earthquake is a deep event, then yes, the time interval will always be large. However, that is different than saying that if the time interval is large, the earthquake MUST have been a deep event!

The question asks about a large gap between P and S waves when measured from "a given location." The problem is that we have no idea where that location is in relation to the epicenter of the earthquake. If the location is very close to the epicenter and the gap between P and S waves is large, we can infer that the earthquake was a deep event. However, if the location is far away from the epicenter (e.g., Paris to Berlin), then a large gap could just be the expected result from a regular, more shallow earthquake.

Because we don't how close the "given location" is to the epicenter of the earthquake, we cannot infer that a gap between P and S waves at that point means that the earthquake was a deep event. Eliminate (A).

I hope that helps!
Show more
The passage does not imply that Wadati’s method takes measurements at different locations for the same earthquake. In fact, it indicates the opposite:

    Instead of comparing the arrival times of seismic waves at different locations, as earlier researchers had done. Wadati relied on a time difference between the arrival of primary (P) waves and the slower secondary (S) waves. Because P and S waves travel at different but fairly constant speeds, the interval between their arrivals increases in proportion to the distance from the earthquake focus, or rupture point.

The question becomes where the P and S waves were measured for this particular earthquake. They were measured at a single location, but we don’t know how far away from the epicenter that location was.

As we said in our previous post, if the location of the measurements was near the earthquake, the earthquake was likely deep. But if that location was far from the earthquake, the earthquake may not have been deep. For that reason, we can eliminate (A).

I hope that helps!
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In most earthquakes the Earths crust cracks like porcelain. 27 Nov 2022, 06:41
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Dear Sir,
Could you please explain more for question 9?

I agree that option B undermines the author's explanation. However, I see option E also weaken the author. According to the passage, the explanation is for the quakes at "a depth of more than 50 kilometers". Therefore, if E is true, the explanation is unvalid for all cases below 650km --> undermine the author's explanation

Passage: "The question remained: how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture? Wadati’s work suggested that deep events occur in areas (now called Wadati-Benioff zones) where one crustal plate is forced under another and descends into the mantle. The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture."


9. The author’s explanation of how deep events occur would be most weakened if which of the following were discovered to be true?
(A) Deep events are far less common than shallow events.
(B) Deep events occur in places other than where crustal plates meet.
(C) Mantle rock is more ductile at a depth of several hundred kilometers than it is at 50 kilometers.
(D) The speeds of both P and S waves are slightly greater than previously thought.
(E) Below 650 kilometers earthquakes cease to occur.
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In most earthquakes the Earths crust cracks like porcelain. 03 Dec 2022, 20:08
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Question 9


TrungTiger
GMATNinja
Dear Sir,
Could you please explain more for question 9?

I agree that option B undermines the author's explanation. However, I see option E also weaken the author. According to the passage, the explanation is for the quakes at "a depth of more than 50 kilometers". Therefore, if E is true, the explanation is unvalid for all cases below 650km --> undermine the author's explanation

Passage: "The question remained: how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too ductile to store enough stress to fracture? Wadati’s work suggested that deep events occur in areas (now called Wadati-Benioff zones) where one crustal plate is forced under another and descends into the mantle. The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture."


9. The author’s explanation of how deep events occur would be most weakened if which of the following were discovered to be true?
(A) Deep events are far less common than shallow events.
(B) Deep events occur in places other than where crustal plates meet.
(C) Mantle rock is more ductile at a depth of several hundred kilometers than it is at 50 kilometers.
(D) The speeds of both P and S waves are slightly greater than previously thought.
(E) Below 650 kilometers earthquakes cease to occur.
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The passage tells us about two types of earthquakes: those that take place "a few kilometers" from the surface, and some that take place "hundreds of kilometers down in the Earth’s mantle."

The author offers an explanation for the deep earthquakes, saying that they occur "where one crustal plate is forced under another." As you've noted, (B) undermines this explanation.

Take another look at the exact wording of (E):
Quote:
(E) Below 650 kilometers earthquakes cease to occur.
Show more
(E) doesn't tell us anything about the author's explanation. It just gives us a range of where these earthquakes occur: somewhere above 650 kilometers in depth. So, it's not that the author's explanation is "invalid" for earthquakes below that depth -- earthquakes just don't happen at all below that depth. The author's explanation could still be perfectly valid for all deep earthquakes that actually occur.

Eliminate (E) for question 9.

I hope that helps!
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In most earthquakes the Earths crust cracks like porcelain. 27 Feb 2023, 00:05
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Hello everyone,

Can anyone give some insights about how to solve Q7 ?

Thanks in advance

Have a great day
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In most earthquakes the Earths crust cracks like porcelain. 27 Feb 2023, 00:26
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Hello everyone,

Can anyone give some insights about how to solve Q7 ?

Thanks in advance

Have a great day
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The passage states that earthquakes can occur deep in the Earth's mantle, where the rock is ductile and flows instead of cracking under stress. These earthquakes occur in areas where one crustal plate is forced under another and descends into the mantle, forming Wadati-Benioff zones. Kiyoo Wadati discovered that the time difference between the arrival of primary (P) waves and slower secondary (S) waves, known as the P-S interval, can be used to identify deep earthquakes.

The passage also states that for most earthquakes, the P-S interval is short near the epicenter and increases with distance, while the intensity of shaking is strongest near the epicenter and weakens rapidly with distance. However, for deep earthquakes, the delay in the P-S interval is long even at the epicenter, and the intensity of shaking is lower but felt over a broader area.

Therefore, the answer is (E) longer P-S intervals and lower peak intensity. This is supported by the information in the passage that deep earthquakes are characterized by longer P-S intervals even at the epicenter, and a lower peak intensity that is felt over a broader area.

Cheers
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In most earthquakes the Earths crust cracks like porcelain. 04 Sep 2025, 08:18
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